Serviceability limit state design: base response of screw injection piles

Screw injection piles are a type of screw displacement pile that use grout injection to displace soil around the pile tip and to reduce the installation resistance on the pile. The process results in lower noise and vibrations compared to a driven pile, whilst creating displacement mechanisms considered beneficial to the pile’s capacity. Yet while these benefits have increased the uptake of screw injection piles in the industry, divergences in design standards means there is no consensus on the axial response of these piles, particularly with regards to their load-displacement response for serviceability limit state design. This paper takes two settlement prediction methods for sandy soils and compares their performance to instrumented load tests on screw injection piles from two different sites. In summary, the results suggest that screw injection piles develop little to no prestressing around the pile base during installation into sand, and a stiffness-based formulation could accurately estimate the pile displacement at both test sites. The formulation presents an effective way of predicting pile displacement, allowing for more benefit to be gained out of proof load tests and providing an efficient means of validating the in-situ pile capacity after installation.